When fabricating devices that are incorporated into microwave applications and tunable filters (referred to hereafter as tunable dielectric devices) including resonators, filters, and phase shifters that are used in constructing phased array antennae, rectennae for conversion of microwave to dc power, and variable capacitors, it is desirable to employ materials that have minimal power losses in the microwave region of 1 GHz–1000 GHz. In addition, it is desirable to use a material that does not require high voltage to achieve the properties required to be effective. Typically, ferromagnetic materials such as ferrites (e.g., cubic Mn—Zn and Ni—Zn) are used for high frequency microwave applications. These magnetic materials rely on electric or magnetic fields to vary the magnetic permeability of the material to tune the microwave properties. However, ferrites are insufficient for the stringent requirements for new antennae and rectennae over a wide frequency range due to high power losses in this region. Moreover, ferrites require high voltage for the electromagnets to achieve the field required for their effectiveness. Similarly, ceramic ferroelectric materials with high electric permittivity (e.g., barium titanate, strontium titanate, barium strontium titanate) also require high voltage to tune microwave properties. In both instances, these types of devices are very costly.
Piezoelectric materials are also potential candidates for microwave device applications. However, these materials are undesirable for use in microwave device applications and as tunable filters because piezoelectric materials undergo a significant physical change, placing greater complexity in device design.
Stevenson et al. (“Small-bandgap endohedral metallofullerenes in high yield and purity,” Nature, Sep. 2, 1999, Vol. 401, pp. 55–57) describe a technique where the introduction of small amounts of nitrogen into an electric-arc reactor allows for the efficient production of a new family of stable endohedral fullerenes encapsulating trimetallic nitride clusters, Erx—Sc3-xN@C80 (x=0–3). The trimetallic nitride template process generates milligram quantities of product containing for example 3–5% Sc3N@C80, allowing isolation of the material and determination of the crystal structure, optical and electronic properties. The Sc3N moiety is encapsulated in a highly symmetric, icosahedral C80 cage, which is stabilized as a result of charge transfer between the nitride cluster and fullerene cage. Their method provides access to a range of fullerene materials whose electronic properties can be changed by encapsulating nitride clusters containing different metals and metal mixtures. Although Stevenson et al. describe trimetallic nitride cluster formation, they fail to provide a specific use for these materials.
Dorn et al. in US Patent Application Publication US 2004/0054151A1 describes trimetallic nitride endohedral metallofullerene derivatives having the general formula A3-nXnN@Cm(R), wherein A is a metal; X is a second metal; n is an integer from 0–3; m is an even integer from about 68 to about 200; and R is an organic group. By varying the organic groups on the exterior of the fullerene cage, the choice of the encapsulated metal complex, and the size of the fullerene cage, one can change the properties of the trimetallic nitride template fullerenes to fit a particular application. For example, these derivatives can have properties that can find utility in conductors, semiconductors, superconductors, or materials with tunable electronic properties such as quantum computers, optical limiters, nonlinear optical devices, ferroelectrics, and dielectrics. However, Dorn et al. fail to describe how these materials could be made into such devices, or that such devices have characteristic properties that can be tuned at voltages of less than about 5 volts. Moreover, Dorn et al. fail to disclose that in order to make these materials tunable, the metals contained within the fullerene cage (A and X) must be different from one another, and n must be an integer from 1–2, not 0–3.
Gimzewski et al. in U.S. Pat. No. 5,547,774 describe the use of endohedral metallofullerenes and derivatives thereof as storage elements. In particular, they describe endohedrally doping the fullerenes so they are switchable between at least two distinct states. Endohedral doping is defined as placing the dopant in the interior of the fullerene's cage. As the different electronic states are separated by a potential barrier, once distorted the molecule retains its current electronic state until the potential barrier is diminished. This is preferably done by applying an external electric field across the molecules. In addition, the electronic state of the material may be stabilized by applying a DC electric field across the molecules. The teaching of Gimzewski et al. is limited to only a single dopant (there is no mention of a charged molecular complex comparable to A3−nXnN) contained within the fullerene cage and also to electronic distortions that result in different electronic states which may or may not result from the movement of the dopant atoms in the fullerene cage (as shown in FIG. 3 of the U.S. patent). Thus, the states are switched not by molecular movement of atoms within the cage but by applying a relatively large potential between the tip of a scanning microscope and the substrate. This induces an electronic potential that enables access to otherwise unavailable electronic states of the molecule. These states result from distortions caused by application of an electric field and, thus, not the molecules within the fullerene cage. Therefore, in order to induce the electronic state, an electric field must be applied. In contrast, the present invention has an inherent molecular dipole that allows for an infinite number of orientations that are controlled by applying an electric field.
An object of the present invention is to provide a tunable device and method for making such device that employs the use of fullerenes encapsulating trimetallic nitride template compounds which are subjected to voltages of less than about 5 volts in order to orient the dipole moments of the bulk material.
Another object of the present invention is to provide a tunable dielectric device and method that employs a material capable of maintaining its physical dimensions when the dipole moment has been oriented.